This invention relates to printer mechanisms. More particularly, the invention relates to printer mechanisms for compact printers in which a stepper motor rotates a type drum and feeds paper and in which type selection, printing, and paper feed are executed in one turn of the type drum (print cycle).
Miniature printers are known in which the driving force is provided by a single stepper motor which turns a type drum to position a type for printing and which also feeds the paper into printing position. In such printers, the step-wise advance provided by the stepper motor is employed in integral multiples to move the type drum the pitch distance between adjacent types in the peripheral direction of the drum. The positions of the types thus correspond to the positions at which the stepper motor can be stopped but not to the driving waveform. As shown in FIG. 10, the driving waveforms of the conventional stepper motor relate to the positions of the type series without relation to the kind of type. Accordingly, when it is desired to restart a conventional stepper motor which has been stopped for printing, it is necessary to base the generation of the waveform which drives the motor in its next step upon a stored version of the waveform which existed at the moment of stopping, thereby resulting in undesirable complexity in the circuit of the stepper motor. Further, because of stored angular momentum, the stepper motor and associated type drum of such systems are subject, after stopping, to residual vibration for a period of time while the stored energy dissipates. When a type is printed under the foregoing condition, printed characters can be improperly aligned with those in adjacent columns, so that the resulting printout has an inferior appearance. While the alignment can be improved by waiting to print until the vibration has ceased, the printing cycle is undesirably prolonged, giving a slow printer speed. Further, when large amplitude vibrations occur, the selected type may be missed by the printing hammer or there may be some other malfunction, and a printing error such as a missing or partially printed character, may result. Also, the known configuration uses a powering mode in which a single pulse of long duration is applied to stop rotation of the stepper motor so that printing can be effected. The known printer thus has the disadvantage of consuming large amounts of power.